A 3-D Stacked High- $Q$ PI-Based MEMS Inductor for Wireless Power Transmission System in Bio-Implanted Applications

This paper presents high-Q factor 3-D stacked MEMS inductors on polyimide substrate for wireless power transmission systems. The 3-D double layer stacked structure was designed, fabricated, and characterized, and self-planarization of polyimide was realized. The 3-D inductor achieves an inductance of 7.189 μH with a high-Q factor of 26.1 at 4.3 MHz. An inductively coupled wireless power transmission system was set up using the 3-D inductor in combination with a solenoid transmitting coil. At the resonant frequency of 1.6 MHz, the peak-to-peak output open circuit voltage could reach 5.2 V with a maximum power transmission efficiency of 11.74% and an output power of 35.5 mW. Effects of the load impedance and transmission distance on the output power were also investigated. Using this wireless transmission system, the driving of an implanted 3-D microelectrode array for neural prosthesis was demonstrated successfully, indicating that this 3-D stacked MEMS inductor design shows promise for applications in supplying power for implanted medical devices.